Another symbolic attribute of the pentagrams (both upward and downward ones) is spiritual transcendence (upward) and spiritual manifestation (downward).
The upward pointing pentagram symbolizes man's pursuit to liberate his spirit (death, heaven, etc). This is somewhat obvious, as the upward/downward point of the pentagram is attributed to the element of spirit, the other four points being attributed to the four other elements of life: Earth, Air, Fire and Water.
Thus, the downward pointing pentagram symbolizes man's acceptance and perfection of the material world and all the experiences therein. It's not so much a denial of the spiritual. It's just that the Satanist prefers to indulge in the here and now. An acceptance of the physical.
Also, there's the goat (baphomet) within the Satanic pentagram. In one sense, this is the scapegoat. The goat is also a symbol of the mastery of the Earth. There's also much metaphor in the two horns, representing the duality of life: hate/love, pain/pleasure, etc.